Urolithiasis in the Rat

Urolithiasis was investigated in the NMRI-D strain of rat fed a purified type of diet containing 15% casein and 4% salts. The predominant component of the stones produced was calcium citrate. Although previous studies indicated that increased dietary protein eliminated calculi, the present study shows that DL-methionine or L-lysine monohydrochloride supplementation are also effective in reducing the occurrence of calculi and together completely prevent the syndrome. The methionine effect is thought to be via the conversion of methionine-sulfur to inorganic sulfate which provides an acidic group in the urine. The lysine monohydrochloride effect also is believed to be due to the acidic group provided, in this case chloride. These suggestions concerning the effects of DL-methionine and L-lysine were supported by experiments in which dietary inorganic sulfate and chloride reduced the proportion of rats which developed calculi.